Smart cards are finding more and more uses in everyday life. As a result any one individual may be in the possession of several cards of this type. In order to avoid the inconvenience resulting from such a multiplicity of cards to be carried, managed and handled, the expedient has been adopted of arranging some of these cards so that they can be used for several functions. A typical case is that of the smart card comprising an electronic purse function and at least one function of acquiring one or more electronic documents such as public transport or parking tickets or for access to a show.
When the same smart card is used for these two functions of payment means and acquisition, these must be installed therein so that they are completely independent of each other and therefore without any possibility of mutual influence and interference. However, the prime need is an absolute certainty that a document acquired corresponds to the money debited for example from the electronic purse, and vice-versa. If a fault in functioning occurs during the acquisition operation, the situation cannot arise in which money has been taken from the electronic purse whereas the document has not been produced and/or stored legitimately and validly in the card or, conversely, in which the document has been produced/validated but the money has not been deducted.